Liquid crystal displays ("LCD's") and other devices in which the electro-optically active element comprises liquid crystal material are well known.
One type of device employs an encapsulated liquid crystal structure in which a liquid crystal composition is encapsulated or dispersed in a containment medium such as a polymer. When a voltage corresponding to a sufficiently strong electric field is applied via an electrode across the encapsulated liquid crystal structure (the "field-on" condition), the alignment of the liquid crystal molecules therein is re-oriented in accordance with the field, so that incident light is transmitted. Conversely, in the absence of such a voltage (the "field-off" condition) the alignment of the liquid crystal molecules is random and/or influenced by the liquid crystal-matrix interface, so that the structure scatters and/or absorbs incident light. The applied voltage at which the structure changes from its field-off condition to its field-on condition is generally referred to as the threshold voltage. Such devices can be used in displays, architectural partitions, automobile sun-roofs, privacy screens, and signs.
Generally, the encapsulated liquid crystal material is applied to a substrate-electrode combination in a fluid, spreadable precursor form and allowed to convert to its final form by evaporation of a solvent or carrier medium, by a chemical reaction such as polymerization, or by a physical change such as solidification upon cooling. An alternative method is to prepare a film or sheet of encapsulated liquid crystal material and then laminate it to the substrate-electrode combination.
Fergason, U.S. Pat. No. 4,435,047 (1984), discloses making an encapsulated liquid crystal device by preparing an emulsion comprising liquid crystals, a containment medium, and a carrier medium, laying a layer of the emulsion onto a substrate-supported electrode, and allowing the emulsion to dry.
Doane et al., U.S. Pat. No. 4,688,900 (1987), discloses the preparation of encapsulated liquid crystal devices by applying a combination of unpolymerized containment medium precursor monomer and liquid crystal onto a substrate/electrode and polymerizing the monomer.
West et al., U.S. Pat. No. 4,685,771 (1987), discloses the preparation of encapsulated liquid crystal devices by a solvent- or temperature-induced phase separation technique.
The prior art methods have a number of limitations. It is difficult to selectively coat only the portions of the device which are actually electro-optically active, i.e., where the electrode material is present, so that in practice almost the entire substrate is coated. Where the electrode pattern is intricate but relatively small in terms of over-all area, a large proportion of the encapsulated liquid crystal material is effectively wasted. They cannot conveniently apply different types of encapsulated liquid crystal materials to different areas of the electrode/substrate combination, for example in making colored displays. Where the substrate is not planar, for example, in automobile sunroofs or certain architectural applications, it is difficult to coat.
I have discovered a new method of applying encapsulated liquid crystal material to electrodes which overcomes the foregoing limitations.